This invention relates to a method for the recycle treatment of nickel plating waste water by means of ion exchange resins.
Recycle treatment of nickel plating waste water by means of ion exchange resins has been previously known. Thus, in the processes practiced to date, nickel plating waste water is allowed to flow over cation resins so as to adsorb nickel ions, and when the cation resins become saturated, the nickel ions adsorbed on the resins is eluted by passing through mineral acids, particularly sulfuric acid, so as to regenerate the said cation resins and, at the same time, to recover nickel salt solutions; in these cases, due to the presence of an excessive amount of sulfuric acid, the eluted solutions, namely the nickel salt solutions, cannot be re-used as a nickel plating solution as such, and therefore, they are further treated over anion resins to remove the excessive acid by adsorption so as to recover reusable solutions.
However, in the course of removing the acid, by means of treatment with anion resins, from the solution eluted from the said cation resins, the nickel ion concentration in the solution drops by about 20% and thus a solution with a desired concentration cannot be recovered; furthermore, a considerable amount of nickel is present in the wash water and has to be removed from the washings of the said anion resins after adsorption by passing the wash water through cation resin beds, thus causing an increased load on the cation resins, and in addition, the amount of alkali required for the regeneration of anion resins is several times greater than the theoretical, thus causing increased secondary pollution of the treatment water, to mention some of the drawbacks.